The field of the invention is cyclic ketones and the present invention is particularly concerned with the production of cycloheptanone from suberic-acid.
The synthesis of cyclic ketones such as cycloheptanone (suberone) has been comprehensively described in the literature. The chemical structure, preparation and physical properties of suberic-acid and cycloheptanone are disclosed in the Kirk-Othmer, "Encyclopedia of Chemical Technology" 2nd Edition, Volumes 1, (1963) Pages 249-250 and 12, (1967) Page 106 respectively and the preparation of ketones is disclosed generally in Volume 12, (1967) at Pages 101-169, the disclosure of which is incorporated herein by reference.
As regards the so-called Dieckmann condensation of cycloheptanone, the reaction of a dicarboxylic acid ester is carried out in the presence of an alkali alcoholate. The maximum yield is about 75% when five- or six-link rings are formed. On the other hand, the use of dicarboxylic acid esters with longer chains (up to C.sub.14) offers only slight yields when this method is employed (J. Org. Chem. 23, 1958, p. 1708).
Comparable yields also are obtained in the cyclization of adipic acid into cyclopentanone. The carbonates of zinc, of cadmium and of manganese are particularly suitable as catalysts. However, when subericacid is used, only a yield of about 40% of cycloheptanone is achieved (Izv. Akad. SSR, 1968, 3, pp. 632-636).
Similarly unsatisfactory values are achieved in the so-called Tiffenaeu-Demjanov ring-widening method. Butadiene and acrylonitrile are converted into 1-cyanocyclohexene-3 which is reduced into the amine and then is diazotized and converted into cycloheptanol. The cycloheptanone (suberone) is then available through dehydration of the cycloheptanol.
Substantially superior yields up to about 95% are achieved in the Ziegler condensation. However, this reaction requires equimolar quantities of alkylated alkali amides in solutions as dilute as possible (Ann. Chem. 504 (1933), pp. 95-130).